The components are linked to one another via three threaded compression collars, two of which (the drain tube and the p-trap) ride over separate nylon or rubber gaskets. That “J” shaped piece of plumbing at the bottom of your sink drain is called a P-trap (or simply the “trap”). It’s specifically designed to hold or trap water in the pipe after drainage is complete. By shining a light into the drain tube from below, you can get a better perspective on the situation than you might from the sink. Similarly, hair clogs can emanate from the tailpiece tube which connects to the drain system within the house.